H-guide attenuator



Nov. 3, 1964 L. BIRENBAUM H-GUIDE ATTENUATOR File d Dec. 6, 1962 INVENTOR LEQ BIRENBAUM BY M falmm,

United States Patent 3,155,929 H-GUlDE ATTENUATOR lLeo llirenhaum, New York, N.Y., assignor to Polytechnic Institute of Brooklyn, Brooklyn, N .Y., a corporation of New York Filed Dec. 6, 1962, Ser. No. 242,763 Cla ms. (Cl. 333-81) The present invention relates to microwave attenuators and more particularly to a waveguide attenuator for an H-guide.

An H-guide is an electromagnetic waveguide which is composed of a pair of longitudinally extending conductive plates or strips arranged parallel with each other and spaced apart by a distance that is smaller than the width of the plates, a dielectric strip being located between the plates and extending longitudinally along the center lines of the plates. The H-guide is excited with electromagnetic energy in a mode that has its principal electric vector parallel to the plates. For further information on the H-type waveguide, see articles by F. J. Tischer, T he H-Guide, a Waveguide for Microwaves, published in IRE. Convention Record, 1956, part 5, pages 4447; and Tele Tech Magazine for November 1956, pages 50, 51, 130, 134 and 136.

It is a primary object of the invention to provide a microwave attenuator for an H-guide.

Another object is to provide a fixed microwave attenuator that is easy to make and assemble in a section of H-guide.

Still another object is to provide a microwave attenuator embodied in a section of H-guide, and which is ad justable for varying the attenuation of microwave energy.

The foregoing as Well as other objects of the invention are achieved by a microwave attenuator which is composed of a section of H-guide that contains a vane having microwave resistance properties, the vane passing through the dielectric strip of the H-guide and lying in a plane parallel with the guide plates. In the adjustable attenuator, the vane is formed from a disc of dielectric material which carries a series of thin parallel bands of resistance material. The disc is mounted for rotation in its own plane to vary the attenuation of microwave energy propagated through the H-guide section.

The achievement of the foregoing objects as well as other objects and advantages of the invention will become more apparent from the following detailed description and the showing in the drawing wherein:

FIG. 1 is a perspective view of the fixed attenuator embodiment of the invention showing part of the upper plate broken away and showing one end of the dielectric strip cut off;

FIG. 2 is a perspective view of the adjustable attenuato-r embodiment of the invention showing an intermediate part of the upper plate broken away.

Referring to FIG. 1, a section of an H-guide for propagating microwave energy is composed of a pair of longitudinaily extending conductive plates 11 and 12 supported parallel with each other and spaced apart by a distance that is considerably smaller than the width of the plates. The plates 11 and 12 are held in spaced relation by suitable means, such as the plurality of posts or spacers 13 having their ends located in holes spaced along both edges of each plate. These spacers may be of metal or of dielectric material. An L-shaped flange 16 is provided at each end of each plate for attaching the section of H-guide to other sections, not shown.

A dielectric strip 14, having a rectangular cross section, is positioned between the plates 11 and 12 and extends longitudinally along the center lines of the plates. The strip 14 may be made from various dielectric materials including polystyrene, polyethylene and epoxy resins.

However, for the purpose of the present invention, it is preferred to use a cellular dielectric material obtained commercially under the name Polyfoam. Such foams may be made from polystyrene, polyethylene or epoxy resins. For fioamed materials, the width of strip 14 preferably will be larger than the spacing between the plates, but this is not necessary. If the width is smaller than the height, the metal plates must be very much Wider. For solid dielectric materials, the width of strip 14 will be very much smaller than the height. The section of H- guide is adapted to propagate microwave energy in a mode that has its principal electric vector parallel with the plates 11 and 12. This electric vector is referred to in the drawings by the arrow E.

The H-guide described up to this point is of conventional construction, and the various dimensions of the conducting plates and of the dielectric strip, as well as the material of the dielectric strip, are all selected according to well-known considerations, and taking into consideration the frequency band to be transmitted. It is known that the dielectric strip 14 concentrates a major portion of the energy for transmission within the strip, but additional energy is transmitted in the air spaces between the plates 11 and 12 on opposite sides of the strip 14. The proportion of energy transmitted in the strip 14 and in the air spaces may be varied somewhat by varying the dimensions of the strip 14 and the separation between the plates 11 and 12.

To eiiect attenuation of the microwave energy transmitted along the H-guide, the dielectric strip 14 is slit or slotted transversely of the strip from one edge to the other, midway between the plates 11 and 12, as shown by the slot 17. Located within the slit or slot 17 is a thin vane of dielectric material 18 which has resistive properties capable of absorbing microwave energy. For example, the vane 18 may be a thin sheet or strip of dielectric material having one or both faces thereof coated with a thin metallic film applied by any suitable process, such as by thermal evaporation of a suitable metal onto opposite faces of the vane. The lossy vane 18 is supported by strip 14 midway between the plates 11 and 12 in a plane parallel to the plates. The vane 18 passes transversely across the H-guide in the plane of the principal electric'vector of the microwave energy. The opposite longitudinal edges of the vane are parallel and are at right angles with the longitudinal axis of the strip 14. If desired, the resistive value of the vane 18 may be varied in the direction of energy propagation for impedance matching purposes. The lossy vane 18 need not he supported at the midplane between plates 11 and 12, but may be closer to one plate than the other. However, for maximum attenuation, the vane shold be supported at the mid-plane position.

The ends of the vane 18 extend laterally from the strip l4- and into the air spaces between plates 11 and 12. If desired, the ends of vane 18 may be held in place by spacers, not shown, secured to the edge portions of plates 11 and 12.

In operation of the attenuator, shown in FIG. 1, microwave energy is supplied to either end of the section of the H-guide from an external source of electromagnetic Wave energy, and in a manner so that the H-guide is excited in a mode that has its principal component of electric field parallel to the plane of the vane 18, and transversely of the strip 14. Conduction currents are created in the vane 18, and a portion of the energy of the incident wave is dissipated in the form of heat. The attenuation is fixed and is proportional to the length of the vane 18 along the direction of Wave energy propagation. The end portions of the Vans absorb energy from the electric fields in the air spaces on opposite sides of strip 14.

An alternative embodiment of the invention for varying the attenuation along an H-guide is illustrated in FIG. 2, where the same reference numerals are used to refer to parts that serve the same functions as correspondingly numbered parts shown in FIG. 1. Therefore, the details of the similarly numbered parts will not be repeated in the description of F IG. 2.

The construction of FIG. 2 is substantially the same as in FIG. 1, except for the construction of the attenuator vane. In this case, the lossy vane located within the slot 17 is in the form of a disc 21 formed of a thin disc of dielectric material having one or both faces covered with thin parallel strips 22 of resistive material which re insulated from each other. This attenuator vane may be formed of a very thin disc of mica or glass and the lossy strips 22 may be of thin metal film strips applied by any suitable process, such as by thermal evaporation of a suitable metal upon the faces of the disc through a suitable shield or 135k to form separate strips. lternatively, the strips may be formed from a continuous film coating by groovin or scoring the coating into separate strips.

The attenuator disc 21 is suitably mounted within slot 17 for rotation about its axis and is held in place for mechanical stability by suitable supports located outside the H-guide and secured to the edge portions of plates 11 and 12. The disc 21 may be rotated in any suitable manner, as by engaging the thumb with an exposed edge of the disc, to change the orientation of the strips or hands 22 relative to the direction of power propagation of the microwave energy.

In operation of the variable attenuator of FIG. 2, when the disc 21 is turned so that the lossy strips or hands 22 are parallel to the strip 14 of Polyfoam, minimum attenuation is obtained because the principal electric field component E is normal to the lossy bands. The amount of minimum attenuation produced with the resistive strips 22 arranged parallel with the dielectric strip 14 will depend upon the width of the resistive strips and will decrease with decrease in the width of the strips. Preferably strips 22 should be of relatively narrow width so that several strips will be located within the slot 17 when they are parallel with the dielectric strip 14. When the disc is oriented so that the resistive strips or hands are normal to the strip 14, the principal electric field component E is parallel to the resistive strips 22, creating currents in the bands and absorbing wave energy. Consequently, maximum attenuation is produced with the bands 22 normal to the strip 14. A different amount of attenuation is produced by rotating the disc 21 to a different position.

When the lossy bands 22 are neither parallel nor perpendicular to the strip 14, i.e., when the attenuation is between the minimum and maximum values, there is a tendency to excite another propagating mode which has a longitudinal electric field component in the geometric center of the guide. This unwanted mode may be suppressed by incorporating within strip 14, at opposite ends of slot 17, and in the central vertical plane of the strip, two lossy vanes 23a and 231'). Thus, the undesired longitudinal electric fields at the center of the guide (which is not present for the desired mode) set up conduction currents in lossy vanes 23:? and 23b and thereby suppress the unwanted mode.

Preferred embodiments of the invention have been shown and described, but obvious changes could be made in these embodiments without departing from the scope of the invention as defined in the accompanying claims.

1 claim:

1. A microwave attenuator for an H-guide comprising a pair of longitudinally extending conductive plates arranged in parallel relation and spaced apart by a distance smaller than the width of said plates, a dielectric strip positioned between said plates and extending longitudinally along the center lines of said plates, said dielectric strip constituting the wave-guiding element of said H-guide, and a vane having microwave resistance properties, said vane passing transversely through said dielectric strip and lying in a plane parallel with said plates, said l-l-guide serving to propagate microwave energy in a mode that has its principal electric vector parallel with said plates and transversely of the axis of said dielectric strip.

2. A microwave attenuator as set forth in claim 1, wherein said dielectric strip comprises cellular dielectric material selected from the group consisting of polystyreen, polyethylene and epoxy resin.

3. A microwave attenuator as set forth in claim 1, wherein said attenuator vane is a disc carrying on one face thereof a plurality of narrow bands of microwave resistance material arranged in parallel relation, said disc being mounted to be rotated in its own plane for varying the attenuation of microwave energy propagated by said guide.

4. A microwave attenuator as set forth in claim 1, wherein said vane comprises a lossy member of microwave dissipating material having a pair of parallel edges that extend across said H-guide in the direction of the width of said guide.

5. A microwave attenuator as set forth in claim 1, wherein said vane comprises a dielectric disc carrying on one face thereof a series of thin bands of resistance material arranged in spaced parallel relation, said disc being mounted to be rotated in its own plane to vary the attenuation of microwave energy propagated by the H- guide.

6. A microwave attenuator for an H-guide comprising a pair of longitudinally extending conductive plates, arranged in parallel relation and spaced apart by a distance considerably smaller than the width of said plates for holding said plates in spaced parallel relation, a dielectric strip positioned between said plates and extending along the centerlines of said plates, said strip having a rectangular cross section of a width substantially less than the width of said plates and substantially larger than the spacing between said plates, said dielectric strip constituting the wave-guiding element of said H-guide, and a vane having microwave resistance properties, said vane passing transversely through said dielectric strip in a plane parallel with smd plates.

7. A microwave attenuator as set forth in claim 6, wherein the longitudinal edges of said vane are parallel and extend transversely across the space between said conductive plates.

8. A microwave attenuator as set forth in claim 6, wherein said vane is a dielectric disc carrying on one face thereof a plurality of parallel bands of microwave resistance material, said disc being mounted to be rotatcd in its own plane for carrying the attenuation of microwave energy propagated by said guide.

9. A microwave attenuator as set forth in claim 8, wherein said disc is a thin disc of dielectric material upon which has been evaporated said plurality of parallel bands of metallic film.

10. A microwave attenuator according to claim 8 and including two thin vanes of lossy material embodied within said strip of dielectric material on opposite sides of said dielectric disc and arranged along the central longitudinal plane of said strip and normal to the planes of said conductive plates.

References Cited in the file of this patent UNITED STATES PATENTS 2,588,262 Matare Mar. 4, 1952 2,860,368 Bales Nov. 11, 1958 2,909,736 Sommers et al. Oct. 20, 1959 2,961,621 Tanenbaum et al Nov. 22, 1960 2,981, 907 Bundy Apr. 25, 196i 

1. A MICROWAVE ATTENUATOR FOR AN H-GUIDE COMPRISING A PAIR OF LONGITUDINALLY EXTENDING CONDUCTIVE PLATES ARRANGED IN PARALLEL RELATION AND SPACED APART BY A DISTANCE SMALLER THAN THE WIDTH OF SAID PLATES, A DIELECTRIC STRIP POSITIONED BETWEEN SAID PLATES AND EXTENDING LONGITUDINALLY ALONG THE CENTER LINES OF SAID PLATES, SAID DIELECTRIC STRIP CONSTITUTING THE WAVE-GUIDING ELEMENT OF SAID H-GUIDE, AND A VANE HAVING MICROWAVE RESISTANCE PROPERTIES, SAID VANE PASSING TRANSVERSELY THROUGH SAID DIELECTRIC STRIP AND LYING IN A PLANE PARALLEL WITH SAID PLATES, SAID H-GUIDE SERVING TO PROPAGATE MICROWAVE ENERGY IN A MODE THAT HAS ITS PRINCIPAL ELECTRIC VECTOR PARALLEL WITH SAID PLATES AND TRANSVERSELY OF THE AXIS OF SAID DIELECTRIC STRIP. 